In general, a vehicle lamp can switch from a low beam to a high beam or vice versa. The low beam is a beam for illuminating a near field ahead of a vehicle with a predetermined illuminance, and the regulation exists relating to the luminous intensity distribution so as not to dazzle drivers of an on-coming vehicle and a preceding vehicle. The low beam is used mainly in driving in an urban area. On the other hand, the high beam is a beam for illuminating a far and wide field ahead of the vehicle with a relatively high illuminance, and the high beam is used mainly in driving at high speeds on a road where there are few on-coming and preceding vehicles. Consequently, the high beam is much superior to the low beam in visibility for the driver but causes a problem that the drivers of on-coming and preceding vehicles are dazzled.
In recent years, the ABD (Adaptive Driving Beam) technology has been proposed in which a beam pattern of a high beam is dynamically and suitably controlled based on an ambient condition of a vehicle. The ABD technology is a technology used to reduce a risk of dazzling drivers of preceding and on-coming vehicles or pedestrians existing ahead of the vehicle by detecting the existence of preceding and on-coming vehicles or pedestrians ahead of the vehicle and reducing the power of light beams which illuminate areas where the preceding and on-coming vehicles or pedestrians are detected.
A vehicle lamp having an ABD function will be described. FIG. 1 is a block diagram of a vehicle lamp which has an ABD function according to a comparison technology. This comparison technology must not be regarded as a known technology.
A vehicle lamp 1r includes a semiconductor light source 10 and a lighting circuit 20r. In the ABD, a high beam illuminating area is divided into a plurality of or N (N is a natural number of 2 or greater) sub-areas. The semiconductor light source 10 includes a plurality of light emitting devices 12_1 to 12_N which are associated individually with the N sub-areas. The light emitting devices 12 are semiconductor devices such as LEDs (Light Emitting Diodes) or LDs (Laser Diodes) and are disposed so as to illuminate the corresponding sub-areas. The lighting circuit 20r controls individually the on (turning on) and off (turning off) of the plurality of light emitting devices 12_1 to 12_N to thereby change the beam pattern or luminous intensity distribution of the high beam. Alternatively, the lighting circuit 20r PWM (Pulse Width Modulation) controls the light emitting devices 12 at high frequencies to thereby adjust the effective luminance.
The lighting circuit 20r includes a current supply 30r, a plurality of bypass circuits 40_1 to 40_N, and a controller 42. The current supply 30r receives a battery voltage VBAT (also referred to as an input voltage VIN) from a battery 2 via a switch 4 and stabilizes a drive current IDRV which flows to the semiconductor light source 10 to a certain target amount.
The plurality of bypass circuits 40_1 to 40_N are associated individually with the plurality of light emitting devices 12_1 to 12_N. The bypass circuits 40 can be switched on and off. When an ith bypass circuit 40_i is switched on, the drive current IDRV flows not to the light emitting device 12_i but to the bypass circuit 40_i, and the light emitting device 12_i is turned off, while when the bypass circuit 40_i is switched off, the drive current IDRV flows to light emitting device 12_i to turn it on.
An upstream processor (for example, an electronic control unit) 6 which controls the vehicle lamp 1r determines on the sub-areas to be illuminated by the high beam and gives an instruction to the controller 42 of the lighting circuit 20r. The controller 42 controls the states of the bypass circuits 40_1 to 40_N based on a control command from the processor 6. Specifically, the controller 42 selects the light emitting devices 12 corresponding to the sub-areas to be illuminated and switches off the bypass circuits 40 which are parallel to the selected light emitting devices 12 while switching on the bypass circuits 40 which are parallel to the remaining light emitting devices 12.